The possible role of the fetal head and pituitary in fetal development and parturition will be studied in a litter bearing species, the pig. All fetuses will be decapitated at 40 days of gestation in some gilts. We have preliminary evidence demonstrating that this can be done quite easily and that some decapitated fetuses will progress through gestation in nearly all treated litters. The gilts with headless fetuses will be observed for gestation length, parturition and lactation. If parturition is delayed the fetuses will be obtained by laparotomy and examined. If parturition is delayed the number of fetuses allowed to remain intact will be varied from one in one uterine horn only to one in each uterine horn. The position of the headless fetuses in reference to intact fetuses will be varied so that in one experiment headless fetuses will be nearest the cervix and in another positions will be reversed. Intact, control fetuses and headless fetuses will be bled from umbilical vessels at days 55, 65, 75, 85, 95, and 105 of gestation. The blood will be analyzed for testosterone and estrogen concentration. Comparisons will be made between fetuses of the same sex within the same litters.